1. Field of the Invention
The present invention relates generally to a drawing apparatus for performing drawing on a recording material such as a plate mounted on a drum and a method of attaching balance weights for adjusting a balanced state at the time of rotating the drum.
2. Description of the Background Art
A drawing apparatus for performing drawing upon irradiation of various types of photosensitive materials with light has been used. In a drum-type drawing apparatus, a photosensitive material is attached to a recording drum which is rotatable in a primary scanning direction, and a recording head comprising a laser diode and the like is moved in a secondary scanning direction parallel to a rotary shaft of the recording drum, to perform drawing on the photosensitive material.
FIG. 37 is a schematic perspective view of a recording drum of a conventional drawing apparatus. A recording drum 1 shown in FIG. 37 is so constructed that a plate 2 made of aluminum can be mounted thereon as a photosensitive material. A fixing clamp 4 for fixing one end of the plate 2 and a movable clamp 5 for fixing the other end of the plate 2 are provided on an outer peripheral surface of the recording drum 1. The movable clamp 5 is formed so as to be movable on the outer peripheral surface of the recording drum 1 depending on the size of the plate 2. The recording drum 1 to which the plate 2 is attached is rotated at relatively low speed around the rotary shaft 3, so that drawing is performed on the surface of the plate 2.
In recent years, it has been needed to improve the efficiency of drawing processing on the plate 2. Therefore, it has been examined whether the recording drum 1 to which the plate 2 is attached is rotated at high speed to perform a drawing operation.
However, the plate 2 made of aluminum is heavier than a film material or the like, and is attached in an offset state to a part of the outer peripheral surface of the recording drum 1. When the recording drum 1 is rotated at high speed, therefore, a centrifugal force developed by the plate 2 causes an unbalance force to be exerted on the rotary shaft of the recording drum 1. The fixing clamp 4 and the movable clamp 5 are provided on the outer peripheral surface of the recording drum 1. The fixing clamp 4 and the movable clamp 5 respectively have corresponding masses. When the recording drum 1 is rotated at high speed, similarly to the plate 2, therefore, centrifugal forces developed by the fixing clamp 4 and the movable clamp 5 cause an unbalance force.
When the unbalance force 5 caused by the plate 2, the fixing clamp 4 and the movable clamp 5 is exerted on the recording drum 1, forced vibration may occur in bearings for supporting the rotary shaft 3 of the recording drum 1 when the recording drum 1 is rotated at high speed, so that the recording drum may develop a fault. The production of such an unbalance force presents no problem when the recording drum 1 is rotated at low speed, as in the conventional example, while presenting a large problem as the recording drum 1 is rotated at high speed in order to make the drawing operation efficient.
An object of the present invention is to provide a drawing apparatus in which no forced vibration occurs by an unbalance between centrifugal forces at the time of rotation and a method of attaching balance weights.
A drawing apparatus according to the present invention is a drawing apparatus for drawing an image on a recording material, comprising a cylindrical drum having a rotary shaft and an outer peripheral surface, driving means for rotating the drum around the rotary shaft, a fixing member provided on the outer peripheral surface of the drum for fixing the recording material to the outer peripheral surface of the drum, a plurality of balance weights provided so as to be movable and fixable along a circumference whose center coincides with the rotary shaft of the drum, and position calculation means for calculating, on the basis of information relating to the recording material and the fixing member, the positions of the plurality of balance weights for canceling an unbalance force caused by centrifugal forces developed by the fixing member and the recording material at the time of rotating the drum.
In the drawing apparatus, the recording material is mounted on the outer peripheral surface of the cylindrical drum by the fixing member, and is rotated by the driving means. An image is drawn onto the recording material which is rotated as the drum is rotated. The fixing member and the recording material which are provided on the outer peripheral surface of the cylindrical drum respectively develop centrifugal forces in different directions at the time of rotating the drum. Therefore, the unbalance force caused by the centrifugal forces developed by the recording material and the fixing member is exerted on the rotary shaft of the drum.
On the other hand, the plurality of balance weights are provided along the circumference whose center coincides with the rotary shaft of the drum. Each of the balance weights develops the centrifugal force by the rotation of the drum. The plurality of balance weights are arranged such that a composite force of the centrifugal forces developed by the balance weights is balanced with the unbalanced force caused by the recording material and the fixing member. Even when the drum is rotated, therefore, the unbalance force is prevented from being exerted on the rotary shaft. Therefore, it is possible to prevent the drum from developing a fault by forced vibration occurring in the rotary shaft of the drum. The plurality of balance weights are provided so as to be movable and fixable along the circumference whose center coincides with the rotary shaft of the drum. Even when the weight and the size of the recording material are changed, therefore, it is possible to cancel the unbalance force caused by the recording material and the fixing member by changing the positions of the plurality of balance weights.
The position calculation means calculates the positions of the balance weights on the basis of the information relating to the recording material and the fixing member. Even when a different type of recording material is used, therefore, it is possible to calculate the most suitable position of the balance weight depending on the type.
The cylindrical drum may further have two end surfaces disposed on opposite sides thereof, and the plurality of balance weights may comprise at least two balance weights provided on each of both the end surfaces of the drum so as to be movable and fixable along the circumference.
In this case, at least two balance weights are provided on each of both the end surfaces of the drum. Even when the weight and the size of the recording material are changed, therefore, it is possible to cancel the unbalance force caused by the recording material and the fixing member by changing the positions of the balance weights.
An annular groove whose center coincides with the rotary shaft may be formed on each of both the end surfaces of the drum, and the plurality of balance weights may be provided so as to be movable and fixable along the annular groove.
In this case, it is easy to move and position the plurality of balance weights by providing the annular grooves.
Each of the plurality of balance weights may include a magnet which is attractable to each of both the end surfaces of the drum.
The balance weight includes a magnet, thereby making it possible to easily move and fix the balance weights on both the end surfaces of the drum without using a special structure.
The drawing apparatus may further comprise movement means for moving the plurality of balance weights to the positions calculated by the position calculation means.
In this case, the movement means can move the plurality of balance weights. Therefore, it is possible to rotate the drum at high speed without causing forced vibration in the rotary shaft of the drum irrespective of the type of the recording material.
The movement means may comprise engagement means for engaging one of the balance weights provided on the drum, and control means for rotating the drum by activating the driving means in a state where the balance weight is engaged by the engagement means, to move the balance weight to the position calculated by the position calculation means.
The engagement means engages one of the balance weights, to stop the balance weight in the position. In this state, the driving means rotates the drum, thereby making it possible to move the position of the balance weight on the end surface of the drum to a predetermined position.
The drawing apparatus may further comprise storage means for storing the position information of each of the balance weights on each of the end surfaces of the drum, and the control means may rotate the drum by activating the driving means to the position where the balance weight is to be engaged by the engagement means on the basis of the position information stored in the storage means.
In this case, the storage means stores the position information of the balance weights on the end surface of the drum. Therefore, the control means takes out the position information from the storage means, and refers to the position information to rotate the drum, so that the engagement means can easily engage the balance weights.
The drawing apparatus may further comprise detection means for obtaining the position information of each of the balance weights on each of the end surfaces of the drum, and the control means may rotate the drum by activating the driving means to the position where the balance weight is to be engaged by the engagement means on the basis of the position information obtained by the detection means.
In this case, the position information of each of the balance weights on each of the end surfaces of the drum is obtained by the detection means. The control means rotates the drum on the basis of the obtained position information of the balance weight, so that the engagement means can easily engage the balance weight.
The drawing apparatus may further comprise input means for inputting the information relating to the recording material.
The information relating to various types of recording materials are inputted using the input means. The position calculation means calculates the positions of the plurality of balance weights on the basis of the information inputted from the input mean. When a different type of recording material is used, therefore, it is possible to arrange the plurality of balance weights in the most suitable positions irrespective of the type of the recording material by inputting the information.
The position calculation means may calculate, on the basis of the information relating to the recording material and the fixing member, an unbalance amount caused by the recording material and the fixing member, and calculate the positions of the plurality of balance weights such that a weighting amount caused by the plurality of balance weights is balanced with the unbalance amount.
Consequently, it is possible to easily calculate the positions of the plurality of balance weights such that the weighting amount caused by the plurality of balance weights are balanced with the unbalance amount caused by the rotation of the fixing member and the recording material.
The drawing apparatus may further comprise information detection means for detecting the information relating to the recording material mounted on the drum.
In this case, the information relating to the recording material mounted on the drum is detected, and the positions of the plurality of balance weights are calculated such that the unbalance force caused by the centrifugal forces exerted on the drum is canceled on the basis of the detected information. Even when the setting of the information relating to the recording material is erroneous, forced vibration is prevented from occurring in the drum by the unbalance force at the time of rotating the drum.
The information detection means may detect the size of the recording material mounted on the drum.
In this case, the size of the recording material mounted on the drum is detected. Even when the setting of the size of the recording material is erroneous, therefore, forced vibration is prevented from occurring by the unbalance force at the time of rotating the drum.
The drawing apparatus may further comprise unbalance detection means for detecting the presence or absence of an unbalance force caused by the centrifugal forces exerted on the drum.
In this case, the presence or absence of the unbalance force caused by the centrifugal forces exerted on the drum is detected, thereby making it possible to prevent the forced vibration from occurring by the unbalance force at the time of rotating the drum.
The unbalance detection means may comprise driving release means for releasing a driving force of the driving means, to bring the drum into a free state from the driving means, rotation detection means for detecting whether or not the drum is rotated after being brought into a free state by the driving release means, and judgment means for judging the presence or absence of the unbalance force on the basis of the result of the detection by the rotation detection means.
In this case, the driving force of the driving means is released, so that the drum is brought into a free state from the driving means. When the unbalance force exists, the drum is rotated. Therefore, it is possible to judge the presence or absence of the unbalance force by detecting whether or not the drum is rotated.
The judgment means may judge that the unbalance force exists when the rotation of the drum is detected, while rotating the drum through a predetermined angle by activating the driving means and then releasing the driving force of the driving means by the driving release means when no rotation of the drum is detected, and judging that the unbalance force exists when the rotation of the drum is detected, while judging that the unbalance force does not exist when no rotation of the drum is detected.
When the drum is rotated after being brought into a free state, it is possible to judge that the unbalance force exists. Even in a case where the unbalance force exists, when the direction of the unbalance force coincides with the direction of gravity when the drum is brought into a free state, the drum is not rotated. When it is not detected that the drum is rotated, therefore, the drum is rotated through a predetermined angle by the driving means, and is then brought into a free state. When the drum is rotated in this state, it can be judged that the unbalance force exits. When the drum is not rotated in this state, it can be judged that the unbalance force does not exist.
In a drawing apparatus for drawing an image on a recording material while rotating a cylindrical drum on which the recording material is mounted by a fixing member, a method of attaching unbalance weights according to another aspect of the present invention is a method of attaching on the drum a plurality of balance weights for canceling an unbalance force caused by centrifugal forces developed by the recording material and the fixing member at the time of rotating the drum, which comprises the steps of calculating, on the basis of information relating to the recording material and the fixing member, the positions of the plurality of balance weights for canceling the unbalance force, the positions of the plurality of balance weights being determined along a circumference whose center coincides with a rotary shaft of the drum, and attaching the plurality of balance weights to the calculated positions.
In the method of attaching the balance weights, it is possible to attach the balance weights along the circumference whose center coincides with the rotary shaft of the drum such that the unbalance force caused by the fixing member and the recording material is canceled. Consequently, it is possible to perform drawing while rotating the drum at high speed without causing forced vibration in the rotary shaft of the drum.
The plurality of balance weights may be at least two balance weights provided on each of both the end surfaces of the drum along the circumference.
In this case, it is possible to mount at least two balance weights on each of both the end surfaces of the drum so as to cancel the unbalance force caused by the fixing member and the recording material. Consequently, it is possible to perform drawing while rotating the drum at high speed without causing forced vibration in the rotary shaft of the drum.
The step of calculating the positions may comprise the steps of calculating, on the basis of the information relating to the recording material and the fixing member, an unbalance amount caused by the recording material and the fixing member, and calculating the positions of the plurality of balance weights such that a weighting amount caused by the plurality of balance weights is balanced with the unbalance amount.
Consequently, the unbalance amount caused by the recording material and the fixing member is calculated for each drawing processing of various types of recording materials, and the positions of the plurality of balance weights are calculated such that the weighting amount caused by the balance weights is balanced with the unbalance amount. The balance weights are attached to both the end surfaces of the drum on the basis of the calculated positions of the balance weights, thereby making it possible to prevent forced vibration from occurring in the rotary shaft of the drum.
A drawing apparatus according to still another aspect of the present invention is a drawing apparatus for drawing an image on a recording material, which comprises a cylindrical drum having a rotary shaft and an outer peripheral surface, driving means for rotating the drum around the rotary shaft, a fixing member provided on the outer peripheral surface of the drum for fixing the recording material to the outer peripheral surface of the drum, and a pair of balance weights, each of which is provided at each of ends of the drum so as to be movable and fixable along a circumference whose center coincides with the rotary shaft of the drum and a radius of the circumference.
In the drawing apparatus, the recording material is attached to the outer peripheral surface of the cylindrical drum by the fixing member, and is rotated by the driving means. Drawing is performed onto the recording material which is rotated as the drum is rotated. The fixing member and the recording material which are provided on the outer peripheral surface of the cylindrical drum respectively develop centrifugal forces in different directions at the time of rotating the drum. Therefore, the unbalance force caused by the centrifugal forces developed by the recording material and the fixing member is exerted on the rotary shaft of the drum.
On the other hand, the pair of balance weights is provided at each of both the ends of the drum. Each of the balance weights develops a centrifugal force by the rotation of the drum. The pair of unbalance weights is arranged such that the composite force of the centrifugal forces developed by the pair of balance weights is balanced with the unbalance force caused by the recording material and the fixing member. Even when the drum is rotated, therefore, the unbalance force is prevented from being exerted on the rotary shaft, so that the drum can be prevented from developing a fault by forced vibration occurring in the rotary shaft of the drum. The pair of balance weights provided at each of both the ends of the drum is provided so as to be movable and fixable along the circumference and the radius of the drum. Even when the weight and the size of the recording material are changed, therefore, it is possible to cancel the unbalance force caused by the recording material and the fixing member by changing the position of each of the balance weights in the radial direction and the circumferential direction.
The cylindrical drum may further have two end surfaces disposed on opposite sides thereof, and each of the pair of balance weights may be provided on each of the end surfaces of the drum.
In this case, each of the balance weights is provided on each of the end surfaces of the drum so as to be movable and fixable along the circumference and the radius of the drum. Even when the weight and the size of the recording material are changed, therefore, it is possible to cancel the unbalance force caused by the recording material and the fixing member by changing the position of each of the balance weights in the radial direction and the circumferential direction.
Each of the pair of balance weights may include a magnet which is attractable to each of both the end surfaces of the drum.
By composing the balance weights of the magnet, the balance weights can be easily moved on both the end surfaces of the drum and fixed thereto without using a special structure.
The drawing apparatus may further comprise position calculation means for calculating, on the basis of information relating to the recording material and the fixing member, the positions of the pair of balance weights for canceling an unbalance force caused by centrifugal forces developed by the fixing member and the recording material at the time of rotating the drum, and movement means for moving the pair of balance weights to the positions calculated by the position calculation means.
In this case, the position calculation means calculates the positions of the balance weights on the basis of the information relating to the recording material and the fixing member. Even when a different type of recording material is used, therefore, it is possible to calculate the most suitable position of the balance weight depending on the type. Consequently, the movement means can move the pair of balance weights. Therefore, it is possible to rotate the drum at high speed without causing forced vibration in the rotary shaft of the drum irrespective of the type of the recording material.
The position calculation means may calculate the respective positions, along the radius and the circumference, of the balance weights on each of the end surfaces of the drum, and the movement means may comprise engagement means to be engaged with one of the balance weights provided on each of the end surfaces of the drum, the engagement means being movable along the radius, and control means for moving the engagement means to transfer the balance weight to the calculated position along the radius on the end surface of the drum, and for rotating the drum by activating the driving means in a state where the balance weight is engaged with the engagement means, to transfer the balance weight to the calculated position along the circumference on the end surface of the drum.
In this case, the engagement means is engaged with each of the balance weights, and is moved in the radial direction, to define the position, along the radius on the end surface of the drum, of the balance weight. Further, the driving means rotates the drum in a state where the engagement means is engaged with the balance weight, so that the position, along the circumference on the end surface of the drum, of the balance weight is defined. Consequently, the balance weight is moved to a predetermined position on the end surface of the drum, thereby making it possible to cancel the unbalance force caused at the time of rotating the drum.
The drawing apparatus may further comprise storage means for storing the position information of each of the balance weights on each of the end surfaces of the drum, and the control means may move the engagement means and rotates the drum on the basis of the position information stored in the strage means, whereby the engagement means being engaged with the balance weight.
In this case, the storage means stores the position information of the pair of balance weights on the end surface of the drum. Therefore, the control means takes out position information of the balance weights from the storage means, refers to the position information, to move the engagement means in the radial direction, and rotates the drum, thereby making it possible to easily engage the engagement means with the balance weights.
The drawing apparatus may further comprise input means for inputting the information relating to the recording material.
The information relating to various types of recording materials may be inputted using the input means. The position calculation means calculates the positions of the pair of balance weights on the basis of the information inputted from the input means. When a different type of recording material is used, therefore, the information is inputted, thereby making it possible to arrange the pair of balance weights in the most suitable positions irrespective of the type of the recording material.
The position calculation means may calculate, on the basis of the information relating to the recording material and the fixing member, an unbalance amount caused by the recording material and the fixing member, and calculate the positions of the pair of balance weights such that a weighting amount caused by the pair of balance weights is balanced with the unbalance amount.
Consequently, it is possible to easily calculate the positions of the pair of balance weights such that the balance weights are balanced with the unbalance amount caused by the rotation of the fixing member and the recording material.
In a drawing apparatus for drawing an image on a recording material while rotating a cylindrical drum on which the recording material is mounted by a fixing member, a method of attaching balance weights according to a further aspect of the present invention is a method of attaching to the drum a pair of balance weights for canceling an unbalance force caused by centrifugal forces developed by the recording material and the fixing member at the time of rotating the drum, which comprises the steps of calculating the positions where the pair of balance weights, each of which is provided at each of ends of the drum so as to develop centrifugal forces for canceling the unbalance force exerted on the drum, and attaching the pair of balance weights to the calculated positions.
In the method of attaching the balance weights, it is possible to mount the pair of balance weights at both the ends of the drum such that the unbalance force caused by the fixing member and the recording material is canceled. Consequently, it is possible to rotate the drum at high speed without causing forced vibration in the rotary shaft of the drum, to perform drawing.
Each of the pair of balance weights may be provided on each of both end surfaces of the drum.
In this case, it is possible to attach each of the pair of balance weights on each of both the end surfaces of the drum such that the unbalance force caused by the fixing member and the recording material is canceled. Consequently, it is possible to rotate the drum at high speed without causing forced vibration in the rotary shaft of the drum, to perform drawing.
The step of calculating the positions may comprise the steps of calculating, on the basis of information relating to the recording material and the fixing member, an unbalance amount caused by the recording material and the fixing member, and calculating the positions of the pair of balance weights such that a weighting amount caused by the pair of balance weights is balanced with the unbalance amount.
In this case, the unbalance amount caused by the recording material and the fixing member is calculated for each drawing processing of various types of recording materials. Further, the positions of the pair of balance weights are calculated such that the weighting amount caused by the balance weights is balanced with the unbalance amount. The balance weights are attached to both the end surfaces of the drum on the basis of the calculated positions of the balance weights, thereby making it possible to prevent forced vibration from occurring in the rotary shaft of the drum.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.